1. Field of the Invention
Twisting ball flat panel displays or gyricon “electric paper” using bichromal balls are well known as disclosed in U.S. patents to Sheridon (U.S. Pat. Nos. 4,126,854, and 4,143,103). In systems according to these patents bichromal balls, in a matrix between electrodes, acquire a static electric charge with a dipole component by chemical interaction with a charge director solution and can be oriented by application of a voltage to form visible elements of images.
Other mechanisms have been proposed along similar lines while avoiding the need for a charge director. For example, a difference in contact potential between two semiconducting hemispheres has been proposed (see Richley D96005). Still other proposals have been made for using electric materials to form a permanent dipole (no IP yet).
Extensive experimentation has shown poor performance from chemical means, and a lack of methodology in their design. Furthermore, there appears to be a dearth of possible material combinations which will produce the desired results and also be compatible with current manufacturing techniques.
Methods based on permanent polarization have a fundamental problem of conflicting requirements. In order to remove any tribocharge, and to provide some lubrication, the bichromal balls must be immersed in a fluid. Removal of tribocharge is accomplished through neutralization by any residual ionic components of this fluid. These ionic components are inevitable, even if due only to impurities, and their neutralization effects are cumulative. The conflicting requirement results from the fact that these neutralizing ions will also serve to neutralize any permanent polarization which could be incorporated into a ball. Thus, over some amount of time, any ball containing a permanent dipole will acquire ions from the dielectric fluid which will be bound to it and diminish its net dipole.
A threshold mechanism is needed for passive addressing of a display. Some means for obtaining response with some applied voltage, and no response at half that voltage is necessary in order that simple row-and-column addressing may be used to randomly address the display. Experimentally, there appears to be no well-defined threshold mechanism in existing twisting ball displays. Furthermore, the pursuit of a dipole by chemical means does not provide any indication of how one might be obtained.